Mitochondria (mt) play key roles in cellular energy production and cell death. Beta cell function is tightly linked to mitochondria; as both insulin synthesis and glucose stimulated insulin secretion require mitochondrial ATP production. In this context, reports of mitochondrial DNA (mtDNA) mutations associated with diabetes (T2D) pedigrees in humans account for up to 1% of human T2D. However, mutations in mtDNA are not commonly associated with autoimmune Type 1 diabetes (T1D), although a C to A transversion resulting in a leucine to methonine substitution in the mt-ND2 gene has been associated with protection from T1D in both an at risk human population and in crosses of the T1D-prone NOD with T1D-resistant ALR mice. The goal of this application is to understand how this single amino acid change modifies resistance to T1D. Genetic analysis of T1D susceptibility has focused attention on candidate genes controlling aberrant immune cell function with little focus on genes that may contribute susceptibility or resistance at the ? cell level. Pancreatic islets from the ALR mouse strain maintain an unusual genetic resistance to functional impairment and killing by autoimmune effectors. Our results have linked some of the ALR-derived T1D resistance to mt- Nd2a. While this allele does not prevent the development of spontaneous T1D when introgressed into the NOD genetic background, the ALR-derived genetic variant does in fact protect beta cells from destruction by cytotoxic T lymphocytes as well as combined cytokines. We have determined that this resistance stems from the inability of pro-apoptotic stress to induce mt reactive oxygen species. Our goal is to understand the role this gene plays in ? cell resistance to autoimmune killing. In specific aim 1 we will determine the mechanism by which mt-Nd2a encoding ? cells and primary islets resist destruction mediated by members of the Tumor Necrosis Factor Receptor family, TNFR1 and Fas. Aim 2 will extend the studies to determine the mechanisms utilized by mt-Nd2a encoding islet cells to avert lysis by CTL. Specific aim 3 will use human islets to confirm mechanisms of resistance to ? cell destruction as well as cybrid human ? cells to test if the human alleles of mt-ND2 alter the characteristics of human ? cell death. The studies, as proposed, will provide meaningful data on both the early apoptotic signals that result in human beta cell death as well as insights into how ND2a protects human beta cells.